Quality control of electrostatic image developer mix

ABSTRACT

Apparatus for effecting development of an electrostatic latent image comprising a plurality of magnetic developing rollers positioned with intersecting magnetic force fields for effecting a blanket of developing material extending about and between the developing rollers adjacent an electrostatic latent image bearing surface. The apparatus differs from prior practice in that the mix is not removed from the back side of the rolls, but rather is deliberately established in that area, and is caused to sequentially stand in a brush array, turn flat as it moves to an adjacent roller, flip over to an upright position again, and repeat for the number of rolls involved. As such renewal mixing takes place on the back side of the rolls, a renewal supply is caused to cascade over the back to become entrapped with the old mix carried over from the front.

United States Patent 11 1 Andrako 1 1 QUALITY CONTROL OF ELECTROSTATIC IMAGE DEVELOPER MIX [75] Inventor:

' Ohio [7 3] Assignee: Addressograph-Multigraph Corporation, Cleveland, Ohio [22} Filed: Mar. 2, 1973 [21] Appl. No.: 337,340

52 us. c1 118/637, 117/175, 118/636 51 1111. c1 G03g 13/00 581 Field 61 Search 118/623, 624, 636, 637;

56 References Cited UNITED STATES PATENTS 3,357,402 12/1967 Bhagat 118/637 3,537,427 11/1970 Sato 118/637 3,575,139 4/1971 Nuzum 118/637 3,638,614 2/1972 Young et a1. 118/637 3,641,980 2/1972 Bickmore 118/637 3,707,947 1/1973 Reichart, Jr. 118/637 3,724,422 4/1973 Latone et a1 118/637 Thomas E. Andrako, Maple Heights,

1451 Dec. 24, 1974 Primary Examiner-Mervin Stein Assistant Examiner-Leo Millstein Attorney, Agent, or Firm-Ray S. Pyl; Russell L. Root [57] ABSTRACT Apparatus for effecting development of an electrostatic latent image comprising a plurality of magnetic developing rollers positioned with intersecting magnetic force fields for effecting a blanket of developing material extending about and between the developing rollers adjacent an electrostatic latent image bearing surface. The apparatus differs from prior practice in that the mix is not removed from the back side of the rolls, but rather is deliberately established in that area,

and is caused to sequentially stand in a brush array,

turn flat as it moves to an adjacent roller, flip over to an upright position again, and repeat for the number of rolls involved. As such renewal mixing takes place on the back side of the rolls, a renewal supply is caused to cascade over the back to become entrapped with the old mix carried over from the front.

2 Claims, 5 Drawing Figures QUALITY CONTROL OF ELECTROSTATIC IMAGE DEVELOPER MIX BACKGROUND OF THE INVENTION This invention relates to the development of electrostatic latent images and, in particular to an apparatus for developing electrostatic latent images utilizing a magnetizable carrier materialand an electroscopic toner powder.

More specifically, this invention relates to a magnetic brush development apparatus having an extended development zone.

In the method of development of electrostatic latent .images by the application of electroscopic toner powder through the use of magnetizable carrier material, referred to in the art as magnetic brush development, there is generally employed a single magnetic brush closely spaced adjacent a surface carrying latent electricalcharges in image configuration. For example, see Fisher U.S. Pat. No. 2,904,000.

As the electrostatigraphic art has progressed, the time in which the latent image is in contact with the development system has decreased because of the increased linear speed of the latent image bearing circuit. Therefore, many attempts have been made to increase the length of this development zone as shown, for example by Toku Hojo et al'. U.S. Pat. No. 3,318,284. Large single drum brushes are also used. A factor which plays a part in limiting the speed of the developer assembly using magnetic brush development is the throw off of dry toner from the rotating cylinder when the rotational speed of the cylinder is increased to accommodate a greater number of copy sheets in a given time, as well as the speed at which toner powder is able to be replenished to'the toner mixture container of the assembly. This invention employs the principles of using plural smaller rollers and rotating the brushes in a direction counter to the plate-direction.

The Hojo developer employs two entirely separate development brushes in order to have the image brushed twice at two separate stations. A later effort to decrease the size of the equipment is shown in Young et al U.S. Pat. No. 3,638,614. Ostensibly, according to Young et al, the mere placement of two magnetic brushes adjacent one another is only conditionally satisfactory, and they taught the use of a small intermediate roller between the two rollers to thus provide a means positioned between the plurality of spaced cylinders and adjacent the support surface, The support surface is the drum or paper surface to be toned. The intermediate roller will thereby support the magnetizable developer material in brush-like tuffs in response to the magnetic field emitted through the cylinders.

However, a patent issued to Michael Stanley, U.S. Pat. No. 3,697,050 shows and teaches four roller brushes without the need for any means positioned between the plurality of cylinders for supporting the magnetizable material.

SUMMARY OF THE INVENTION The purpose of this invention is to create a magnetic blanket completely encompassing a plural roll magnetic brush assembly beginning along the face of one roller brush, bridging to the next and any subsequent roller brushes, and carrying overto the back of the final roller and then proceeding down the back of the entire set to the beginning point.

It is the intention, while causing the magnetic blanket to migrate from face to face to create a thorough mixing of the toner mix. This is done by placing the roller brushes substantially in contact with one another, with internal magnets of sufficient strength that the magnetic material is caused to bridge substantially straight across between rollers without any substantial sag of the material away from contact with the device being treated. The space between the rollers remains open without any support roller required.

It is an object of the invention to continue the mixing of toner by allowing the toner mix to proceed down the inactive back side of the roller brush assembly. The mix turns and mixes between each roll by reason of the closely spaced rollers and strength of magnets. Then, by cascading an abundance of fresh toner mix on the back side in greater quantity that the brush roller magnets are capable of holding, new material is intermixed with the old as the turning and mixing takes place.

It is a further object of the invention to allow the excess of old and new toner mix to drop to the bottom of a container whereat it is scooped from the container bottom and lifted to the top for cascading, and causing the fresh material to cascade over a static mixing bridge in order that further mixing and transporting of the mix is assured but without mechanical compression and wearing of the toner mix.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a mechanical schematic of an automatic xerographic reproducing machine utilizing the present invention;

FIG. 2 is a view taken along the line 2-2 of FIG. 1 illustrating the static mixing device of this invention;

FIG. 3 is a schematic illustration of the magnetic brush array with the toner mix accurately illustrated on the surface thereof; v

FIG. 4 is a view of the end of a roller brush showing the adjustable magnet support; and

FIG. 5 is a top view of the roller and magnet support.

DESCRIPTION OF THE PREFERRED I EMBODIMENT The electrostatic copy art is so thoroughly known that no effort is made to illustrate a complete working machine. There are many issued patents and technical journals which completely illustrate such systems if reference is needed. As in all electrostatic systems of the type under consideration, a light image of an original to be reproduced is projected onto the sensitized surface of a plate, whether that plate is a metal plate for later transfer of an image ora paper having a photoconductive insulating-surface. It is immaterial to this invention which plate is used. An electrostatic latent image is formed on that plate. Thereafter, the latent image is developed with an oppositely charged developing material comprising carrier beads and smaller toner particles triboelectrically adhering thereto to form a powder image, corresponding to the latent image on the plate surface. The powder image is then electrostatically fused either directly upon the surface where created, or

transferred to a carrier upon which it is to be permahere as toner and a carrier of larger beads removed in the triboelectric series from the toner so that a triboelectric charge is generated between the toner powder and the granular carrier. The carrier is magnetizable and also provides mechanical control for the formation of the brush bristles by virtue of magnetic fields so that the toner can be readily handled and brought into contact with the exposed surface. The toner is then attracted to the electrostatic latent image from the carrier bristles to produce a visible powder image on an insulating surface.

FIG. ll illustrates a substantially familiar arrangement of an electrostatic toning apparatus wherein there is a drum which represents a photoconductive metal drum or the carriage for a sheet of photoconductive paper, for example.

The illustrated apparatus includes a four cylinder development station 12 which is the principal subject of the present invention. The individual rollers of the station are substantially conventional in form and comprise nonmagnetic rollers 14 which are driven in the same clockwise direction in the FIG. 1 by a drive mechanism consisting of gears or chain driven sprockets, for example but which are not illustrated in this drawing.

Each of the rollers 114$ is provided internally with a magnet system 16 of essentially conventional general arrangement but specifically designed for this invention in the dimension and arrangement of the parts. In this case, the magnet system 16 is comprised of a carrier 17 with a one-half inch square iron magnet 18 facing the drum 10. This side will hereinafter be referred to as the face side or the front side of the roller.

The opposite or back side of the roller is under the influence of a V2 by 1 inch ferritic iron magnet. As the FIG. 3 indicates, the magnets are arranged in opposite polarity from adjoining rollers in order to establish a flux field which bridges from one magnet to the other.

Whereas prior art devices, as suggested in the Background of the Invention above, create a sag between the rollers, or require filler rollers, this invention is partially encompassed in the establishment of a strong flux field bridging between the adjacent surfaces of the rollers in order to accomplish at least two very important functions:

1. The magnetic carrier particles are coated with smaller triboelectric toner particles which are wiped away from the magnetic carrier particle upon contact with the oppositely charged image on the drum 10. In order to expose many surfaces of the carrier brush and thus provide the surface of drum 10 with a full brush of available toner particles, the magnetic field causes the brush to stand up in the normal soft tufts 21, but as that tufts is carried along the surface of a roller 14 and the brush structure meets the bridge flux going to the subsequent adjacent roller, the brush structure will lie down and proceed in a substantially horizontal path as opposed to the vertical path previously assumed in the tufts 21. Such a bridge is indicated by the reference character 22 in FIG. 3. Then, when the magnetic structure reaches the next subsequent brush and begins to come under the influence of the next tufts area 21, the brush structure assumes an upright position reversed from that in the previous brush. Hence, as the magnetic toner mix progresses from face to face or from back to back surface of the rollers it is constantly churned and mixed by lying down and standing up and thus assures as complete a wiping of the triboelectric toner particles from the brush structure as possible.

2. While standing, lying, and restanding, across the face of a plurality of rollers, the surface being toned which passes thereby is exposed to a multitude of different opportunities to pick up toner from a complete moving flow of a dynamic stream of developer mix.

In order to make possible the best arrangement of the magnetic field, the carrier 17 is mounted on an adjustable attitude control lever 23 as shown in FIGS. 4 and 5.

Prior art devices have shown paddle wheel impellers or augers to stir and mix magnetic toner mix in a sump 26. It has been found that the toner mix is sometimes subject to excessive wear when mechanically agitated to any degree and therefore an old and well known bucket system is employed with this invention, but in a somewhat novel manner. Refer to FIG. 1. A bucket conveyor 24 is shown with buckets 25 to lift material from a sump area 26 and cascade the material down over the backside of the rolls in the development station 12. Note, however, that the location of the conveyor is such that the buckets tend first to lose their mix at the top of the uppermost chain sprocket. Therefore, a cross mixing baffle 27 is placed directly over the shaft of the upper drive sprocket in order to cause the spilled toner mix to mix and cross mix and to thus assure a more even distribution of the toner particles. That which does not fall on the cross mixing baffle will spill and fall generally in the area of the back face of the development station and be picked up by the magnetic field along with that material which is carried around the end of the last roller in the series and is returning down the back of the brush array.

The strength of the magnets within the brush array are designed to create a strong arch bridge 22 in order to prevent sagging without the need of auxiliary rollers, but the strength of the magnet is limited. Thus when the material cascades down over the back of the develop ment station there will be some physical dislodgement of the mix being carried by the rollers 14 and new material taking its place. Thus, another aspect of this invention is involved in the fact that the moving blanket of material, turning and churning down the backside of the roller array not only further mixes the exhausted brush structure elements with toner available from neighboring elements, but actually picks up fresh material and/or is dislodged and replaced by fresh material cascading along the backside of the array in the developer station.

A doctor blade 30 establishes the proper height brush structure to control the amount of toner mix which enters the developer station 12.

Finally, as the developer mix is depleted, a fine dust of replacement toner without magnetic material is caused to cascade from a supply 32 and become admixed into the entire system as it floats and falls down into the cascading material being dumped from the buckets 25.

What is claimed is:

l. A magnetic brush apparatus for applying developing material to electrostatic latent images in a electrostatic printing machine of the type utilizing a moving photoreceptor surface, comprising;

a plurality of magnetic developing brushes each having a roller with a periphery upon which bristles of magnetic developing material are adapted to be formed.

said rollers each having an axis of rotation, said axis being substantially parallel to the path of the photoreceptor surface and aligned in a vertical array;

said rollers having a clear space therebetween and internal magnets within the rollers oriented in opposite polarities in one roller from that in the other and establishing a merging magnetic field bridging between the roller brushes to establish a continuous migrating magnetic blanket which accepts magnetic powder material at the first roller and transports the magnetic material between the rollers and the photoreceptor surface along the front face of the rollers in brush form and bridges between rollers in reclining array;

means for removing a portion but less than all of any magnetically attracted material from the topmost of the rollers in the vertical array whereby the remainder of the material will cling to that roller and proceed along the roller on the side thereof oppoas defined in claim 1, wherein there are a series of four rotor brushes aligned with said photoreceptor surface,

each of the rotor brushes has a composite inner magnetic system composed of a one-half inch square cross section iron magnet extending the length of the roller facing the photoreceptor, and a V2 by l inch cross section iron magnet facing the opposite or back side of the roller, and the magnetic system mounted on an adjustable attitude control lever for tuning the bridging magnetic systems with respect to one another. 

1. A magnetic brush apparatus for applying developing material to electrostatic latent images in a electrostatic printing machine of the type utilizing a moving photoreceptor surface, comprising; a plurality of magnetic developing brushes each having a roller with a periphery upon which bristles of magnetic developing material are adapted to be formed. said rollers each having an axis of rotation, said axis being substantially parallel to the path of the photoreceptor surface and aligned in a vertical array; said rollers having a clear space therebetween and internal magnets within the rollers oriented in opposite polarities in one roller from that in the other and establishing a merging magnetic field bridging between the roller brushes to establish a continuous migrating magnetic blanket which accepts magnetic powder material at the first roller and transports the magnetic material between the rollers and the photoreceptor surface along the front face of the rollers in brush form and bridges between rollers in reclining array; means for removing a portion but less than all of any magnetically attracted material from the topmost of the rollers in the vertical array whereby the remainder of the material will cling to that roller and proceed along the roller on the side thereof opposite said front path, allowing the retained material to migrate along the back side of the said array in tHe same form and action as the front but in the opposite direction; and a cascade delivery system for supplying fresh mixture of developer material downward and against the back side of said array.
 2. Apparatus for developing a photoreceptor surface as defined in claim 1, wherein there are a series of four rotor brushes aligned with said photoreceptor surface, each of the rotor brushes has a composite inner magnetic system composed of a one-half inch square cross section iron magnet extending the length of the roller facing the photoreceptor, and a 1/2 by 1 inch cross section iron magnet facing the opposite or back side of the roller, and the magnetic system mounted on an adjustable attitude control lever for tuning the bridging magnetic systems with respect to one another. 